Achieving both macroscopic homogeneity and nanoscale heterogeneity for non-stoichiometric multinary compounds is a critical challenge for the success of copper indium gallium selenide (CIGS) photovoltaic cells. Co-evaporation yields world record performance, but is also a high-temperature vacuum process that is difficult to scale. Here, we consider reactive transfer processing (RTP), which has been developed by Heliovolt as an alternative. ...